The present invention is concerned with a developer for use in dry electrophotography.
The electrophotographic method generally known as xerography utilizes a light-sensitive member in the form of a drum, which is prepared by vapor-depositing a photo-conductive material such as amorphous selenium or a selenium based alloy on an electrically conductive support comprised of copper, aluminum, or the like. The light-sensitive member is charged and exposed to light to form an electrostatic latent image on the surface thereof, which is then developed by the cascade method, the magnetic brush method, the fur brush method, or the like to obtain a visible toner image. The visible image is transferred to a suitable support by the application of an auxiliary electric charge or by corona discharge, and at the same time any untransferred toner remaining on the surface of the light-sensitive member is removed by a cleaning treatment. The light-sensitive member is repeatedly used in the manner described.
According to the cascade developing method, the developer is scooped from a reservoir by buckets provided on an endless conveyer and is dropped onto a light-sensitive member, on which an electrostatic image has been formed, to thereby develop the electrostatic image. Thereafter the developer is removed from the light-sensitive member and returned to the reservoir.
In the magnetic brush method developers containing toners and magnetic carriers are attracted by a magnet in the form of a brush. The light-sensitive member on which an electrostatic image has been formed is rubbed by the brush, whereby the developers are attracted onto the electrostatic image owing to its electrostatic attracting force, thereby developing the electrostatic image.
Although the developers used in these methods are durable for many thousands of repeated uses, the carriers contained in the developers deteriorate owing to mechanical collisions between carrier particles, frictional wear and erosion of the carrier surface, toner adherence to the roughened carrier surfaces, etc., when used for a long period of time. Such deterioration of the carrier changes the friction charging characteristics thereof, i.e. the "tribo electric property", and adversely influences the quality of the copy obtained, thus making it necessary to change the carrier frequently, and thereby incurring much labor and cost.
In continuously supplying conventional developers to a copying machine, contact impulse is caused with the developers remaining in the copying machine, particularly among toners attached to the surface of carriers owing to friction charging. The toners are influenced by friction charging, which is not desired from the standpoint of forming an image. Also, the toners attach to the inside of the copying machine and much labor is needed for sweeping away the toner particles.
Moreover, conventional light-sensitive members are subject to the so-called deletion phenomenon due to external causes at the stage of charging. Deletion phenomena refers to toner filming on the surface of the photo-sensitive materials, and the attachment of air borne impurities and contaminants to the surface. Thus, images obtained are locally blurred. When such deletion occurs, the light-sensitive member is cleaned with an organic solvent, such as isopropyl alcohol, or the like. However, it is difficult to completely solve the problem by cleaning. Consequently, it is conventional to change the light-sensitive member, which is very expensive.
With conventional light-sensitive members the residual developer is removed with a brush made of a synthetic fiber such as nylon, cellulose, or the like, or wool, or with a blade made or urethane rubber. However, since it is difficult to completely remove the developer on the light-sensitive member by these methods, the developer remaining on the light-sensitive member after cleaning causes the copier to make dirty copies or gives rise to the deletion phenomenon, thereby deteriorating the photo-conductivity and charging properties of the light-sensitive member. Therefore, the surface of the light-sensitive member has hitherto been ground with an abrasive solution prepared by dispersing an abrasive such as strontium sulfate, barium sulfate, or the like in an organic solvent to thereby remove the deposited or attached developer. However, there is a fear that use of the above abrasive and organic solvent may be detrimental to the operator's health.